The present invention relates to a terminal device having a radio communication system capable of carrying out a communication between terminals using an infrared optical communication system, and more particularly to a terminal device having a detector for the movement of a person, a substance, or the like using an infrared optical communication system.
Description of the Related Art
In recent years, there have been available terminal devices of a pocket telephone or other communication equipment, in which information can be mutually communicated between terminals using an infrared optical communication circuit. In one terminal device, the infrared optical communication circuit modulates information as optical signals and the modulated optical signals are transmitted from a light-emitting device. In the other terminal device, the transmitted optical signals are received in a photo detector and the received optical signals are demodulated to obtain the transmitted information in the infrared optical communication circuit.
However, when actually observing the situation in use of the terminal devices of this kind, the frequency in use of the radio communication is relatively high, but the frequency in use of the communication between the terminal devices using the infrared optical communication system is not so high. Hence, the efficiency in use of the infrared optical communication system supplemented in the terminal device is low, and its capabilities are not fully taken advantage of. After studying improvement of the efficiency in use of the infrared optical communication system many times, the present inventor has found that an open and close of a door, a movement of a person or substance, or the like can be detected using the infrared optical communication system, resulting in improving the capabilities of such terminal devices. In addition, after investigating a burglar prevention system to be built in the terminal device, the present inventor has considered that the infrared optical communication system can be used.